Long-Term Drop in Caribbean Marine Export Productivity with the Demise of the Central American Seaway

Abstract:

The progressive closing of the Central American Seaway ~3-7 Ma substantially altered the surface ocean salinity, nutrient content, and biology of the Caribbean Sea and Eastern Equatorial Pacific Ocean. Data from fossil plankton, reef development and oceanographic models of the shoaling Central American Seaway suggest that there was a distinct change in Caribbean productivity with closure of the seaway, but there has not been a detailed comparison of export production between the two ocean basins. Here we show that export production gradually decreased in the Caribbean starting about 2.7 Ma while remaining relatively stable in the eastern equatorial Pacific. Data are derived from 0-5.3 Ma XRF records of Caribbean Site ODP 999 and Pacific Site ODP 846 at ~600-1000 year resolution. Caribbean export production falls during glacial phases in response to ventilation of the tropical thermocline by increasingly nutrient-starved Glacial North Atlantic Intermediate Water. In contrast, Caribbean production peaks during interglacials when nutrient-rich Antarctic Intermediate Water ventilates the tropical thermocline. Export production in both the eastern Pacific and Caribbean is governed mostly by high latitude nutrient sources as seen in the dominance of high latitude orbital forcing. The gradual intensification of Caribbean oligotrophy may be responsible for the well documented delay in extinction of Caribbean reef associated fauna relative to closure of the central American Seaway. The increasing nutrient starvation of the Caribbean during glacial events may also have rendered Caribbean reef corals unusually susceptible to anthropogenic nutrient loads in modern times.